Thermocouples and sample probes for combustion studies

Experimental and kinetic modeling study of 1-hexanol combustion in an opposed-flow diffusion flame

“…As suggested by Shaddix [59], a non-catalytic coating can be applied to the thermocouple to reduce the catalysis-induced heating and the use of sufficiently long thermocouples will help minimize conduction loss. A thermocouple length-to-diameter ratio of at least 200 is recommended in literature [60]. The ratio of thermocouple length to diameter in this experiment is over 3300.…”

“…The catalytic heating on the thermocouple has been commonly attributed to the effects of radical recombination near the thermal boundary layer on the wire [60]. Coatings on thermocouples are typically used to reduce or eliminate the effect of catalytic activity on the thermocouple surface.…”

“…Alumina-based coatings have also been used on R type thermocouples as discussed by Heitor and Moreira [60]. Burton et al [93] applied an aluminum oxide/potassium silicate (Al 2 O 3 /K 2 SiO 3 ) coating, which is non-toxic, stable at high temperatures and shown to eliminate catalytic heating.…”

Advanced combustor design concept to control NOx and air toxics

“…The ideal probe provides a sample that is representative of the gas species' concentrations at the point in the combustor where the probe tip is located. However, according to Heitor and Moreira (1993), the accuracy of measurements taken with sample probes can be influenced by "(1) probe-induced fluid dynamic disturbances and composition biasing due to nonisokinetic sampling; (2) the efficiency of quenching; (3) the catalytic effects on the probe surface; and (4) the type of averaging given by the probes." They include multiple references in their paper to studies relating to each of these sources of error.…”

“…In such a case, Heitor and Moreira (1993) suggest that interference effects can be kept as low as 3% if both the probe tip diameter and the upstream diameter of the stream tube entering the probe are smaller than 10% of the characteristic length scale of the flow.…”